1. Field of the Invention
This invention relates to thermally-responsive record material. It more particularly relates to such record material in the form of sheets or rolls coated with color-forming material comprising chromogenic material (electron-donating dye precursor) and acidic color developer material. This invention particularly concerns a thermally-responsive record material (thermal record material) capable of forming a non-reversible image resistant to fade or erasure. The invention teaches record materials having improved thermal response, image formation, image retention and/or image density.
2. Description of Related Art
Thermally-responsive record material systems are well known in the art and are described in many patents, for example U.S. Pat. Nos. 3,539,375; 3,674,535; 3,746,675; 4,151,748, 4,181,771; 4,246,318; and 4,470,057 which are hereby incorporated by reference. In these systems, basic chromogenic material and acidic color developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit the said materials to react, thereby producing a colored mark.
Thermally-responsive record materials have characteristic thermal responses, desirably producing a colored image upon selective thermal exposure.
In the field of thermally-responsive record material, thermal response is defined as the temperature at which a thermally-responsive material produces a colored image of sufficient intensity or density. The desired temperature of imaging varies with type of application of the thermally-responsive product and the equipment used in the imaging process. The ability to shift the temperature at which thermal image of sufficient intensity or density is produced for any given combination of chromogenic material and developer materials is a much sought after and very valuable feature. For example, recent advances in high speed text or image recording demand both high speed recording devices and corresponding thermally-responsive recording materials with sufficient thermal response that are capable of producing a high intensity or high density color image at low thermal energy.
Also, in the field of thermally-responsive record material, the ability to increase the efficiency of the thermal image formation process has decided advantages. First among these is the ability to obtain the same image intensity or density with lower amount of reactants or, alternatively, to obtain a more intense image with the same amount of reactants.
It is an object of this invention to provide a thermally-responsive material having enhanced image intensity or density and/or improved thermal response.
The present invention is a novel thermally-responsive record material comprising a support having provided thereon in substantially contiguous relationship an electron donating dye precursor, and acidic developer material, a compound of the formula 
wherein in formula I, R1, R2 and R3 are independently selected from hydrogen, alkyl, alkoxy, aryl, aralkyl, aralkoxy, halogen, alkoxyalkoxy, alkoxyalkoxy, and aralkoxyalkoxy groups;
wherein in formula I, R4 is independently selected from alkoxyalkyl, alkoxyalkoxy, and aralkoxyalkoxy groups,
and a suitable binder therefor. More preferable R4 is independently selected from alkoxyalkoxy and aralkoxyalkoxy.
In the context of the present invention in formulas I and II the alkyl moieties in the alkyl, aralkyl, aralkoxy, alkoxyalkyl, alkoxyalkoxy and aralkoxyalkoxy preferably are each independently eight carbons or less, and more preferably from one through four carbons. Substituents on aryl moieties in aryl, aralkyl, aralkoxy, and aralkoxyalkoxy groups can each independently include hydrogen, alkyl, alkoxy and halogen. The alkyl group in these substituents also is each independently eight carbons or less, and more preferably from one through four carbons.
In formula 1, it should be understood that substituents R1, R2, R3 and R4 are intended and shown as being able to be attached to any of the carbons identified in formula 1 clockwise numbered 1 through 8.
More particularly the invention is a thermally-responsive record material comprising a substrate having provided thereon in substantially contiguous relationship an electron donating dye precursor, an acidic developer material, a compound of the formula: 
and a suitable binder therefor.
An even more particular class of thermally-responsive record material of the invention comprises a substrate having provided thereon in substantially contiguous relationship an electron donating dye precursor, an acidic developer material, and a compound of the formula: 
wherein R1 and R2 and R3 are each independently selected from hydrogen, alkyl, alkoxy, aryl, aralkyl, aralkoxy, halogen, alkoxyalkoxy and aralkoxyalkoxy groups,
wherein R5 is independently selected from alkyl and aralkyl
said alkyl moieties of the alkyl, alkoxy, aralkyl, aralkoxy, alkoxyalkoxy and aralkoxyalkoxy groups each independently being from one to eight carbons,
said aryl moieties of the aryl, aralkyl, aralkoxy and aralkoxyalkoxy groups each independently being unsubstituted or substituted by alkyl (C1-C8), alkoxy (C1-C8) or halogen,
and a suitable binder therefor.
Some of the more particular halogen substituted variations of formulas I, II, III or IIIa can include: 
wherein x is hydrogen, chlorine or bromine and a suitable binder therefore.
The thermally responsive record material of the invention has the unexpected and remarkable properties of enhanced image intensity or density, and/or improved thermal response. The compounds disclosed herein in formula I, II, III and IIIa desirably function as sensitizers or modifiers facilitating reaction between the mark forming components yielding a more intense image at lowered temperatures or faster imaging.
In the field of thermally-responsive record material, thermal sensitivity (response) is defined as the temperature at which a thermally-responsive material produces a colored image of satisfactory intensity (density). Background is defined as the amount of coloration of a thermally-responsive record material before imaging and/or in the unimaged areas of an imaged material. The ability to maintain the thermal sensitivity of a thermally responsive material while reducing the background coloration is a much sought after and commercially valuable feature.
These and other advantages are obtained from these compounds of the invention.
Increases in thermally-responsive material have been achieved through the incorporation of a sensitizing material in the color-forming composition along with the chromogenic material and acidic developer material. Examples of sensitizing materials are as follows: fatty acids such as stearic acid and behenic acid, amides of fatty acids such as stearamide, metallic salts of fatty acids such as zinc stearate, aluminum stearate, calcium stearate, zinc palmitate and zinc behenate, 4-benzylbiphenyl, triphenylmethane, benzyl 4-benzyloxybenzoate, 2-benzyloxynaphthalene, phenyl 2-naphthoate, 1,2-diphenoxyethane, 1,2-bis (3-methylphenoxy)ethane, 1,2-bis(4-methylphenoxy)ethane, 4-hydroxyoctadecanilide. The compounds of the invention are a new class of sensitizers.
Compounds illustrative of the invention according to formula I, II, III and III(a) include without limitation: 
In general, the compounds according to formulas I, II, III and III(a) can be synthesized from a corresponding substituted or unsubstituted benzyloxyalkanol or alkoxyalkanol. R is alkyl or aralkyl.
The alcohol is first converted to tosylate using p-toluenesulfonyl chloride (TsCl) and aqueous sodium hydroxide in 1,2-dimethyxyethane, keeping the temperature of the reaction mixture below 55xc2x0 C. by slow addition of the base. Then, the tosylate is reacted with the corresponding naphthol at 80xc2x0 C. for about five hours to give the final product.
The times and the temperatures in this general protocol are approximate, and the person skilled in the art can readily adjust the reaction conditions, depending on the moieties involved, to obtain the desired product.
More specific illustrative processes for synthesis of the specific compounds according to formulas I, II, III and III(a) are set forth in more detail in the Synthesis Example. This synthetic route is readily adapted by one having skilled in the art to synthesize any of compounds A through U.
In the heat sensitive record material according to the invention, the compound according to formulas I, II, III and III(a) is preferably used in an amount corresponding to 10 to 1000 parts by weight per 100 parts of the electron donating dye precursor though when optionally blended with other sensitizers, the amount of the compound according to formulas I, II, III and III(a) can optionally be used in reduced amounts.
The record material includes a substrate or support material which is generally in sheet or roll form. For purposes of this invention, sheets can be referred to as support members and are understood to also mean webs, ribbons, tapes, belts, films, cards and the like. Sheets denote articles having two large surface dimensions and a comparatively small thickness dimension. The substrate or support material can be opaque, transparent or translucent and could, itself, be colored or not. The material can be fibrous including, for example, paper and filamentous synthetic materials. It can be a film including, for example, cellophane and synthetic polymeric sheets cast, extruded, or otherwise formed. The gist of this invention resides in the color-forming composition coated on the substrate. The kind or type of substrate material is not critical.
The components of the color-forming system are in substantially a contiguous relationship, substantially homogeneously distributed throughout the coated layer or multi layers of material deposited on the substrate.
The term substantially contiguous relationship is understood to mean that the color-forming components are positioned in sufficient proximity such that upon melting, softening or subliming one or more of the components, a reactive color forming contact between the components is achieved. As is readily apparent to the person of ordinary skill in this art, these reactive components accordingly can be in the same coated layer or layers, or isolated or positioned in separate layers. In other words, one component can be positioned in the first layer, and reactive or sensitizer components or the compound according to Formulas I, II, III and III(a) or an acidic developer or color former positioned in a subsequent layer or layers. The coating can optionally be applied to all of the substrate or spot printed on a certain portion. All such arrangements are understood herein as being xe2x80x9csubstantially contiguous.xe2x80x9d
Also, in the field of thermally-responsive record materials, there are well-known modifications in the coating structure. For example, a top-coating layer may be applied over a thermally-responsive layer as a protection for the latter, or a subcoating layer may be applied between the thermally-responsive layer and the support. Furthermore, some thermally-responsive record materials have both the topcoat and the subcoat in their design. The topcoat and subcoat may be either single-layered or multi-layered.
In manufacturing the record material, a coating composition is prepared which includes a fine dispersion of the components of the color-forming system, polymeric binder material, surface active agents and other additives in an aqueous coating medium. The composition can additionally contain inert pigments, such as clay, talc, aluminum hydroxide, calcined kaolin clay and calcium carbonate; synthetic pigments, such as urea-formaldehyde resin pigments; natural waxes such as Carnuba wax; synthetic waxes; lubricants such as zinc stearate; wetting agents; defoamers, and antioxidants. Other sensitizers can also be included. These sensitizers for example, can include acetoacetyl-o-toluidide, phenyl-1-hydroxy-2-naphthoate, 1,2-diphenoxyethane, and p-benzylbiphenyl or any of the sensitizing material listed earlier herein. Optionally, the record material can be topcoated or use subcoats such as insulating layers or hollow spheres. The color-forming system components are substantially insoluble in the dispersion vehicle (preferably water) and are ground to an individual average particle size of between about 1 micron to about 10 microns, preferably about 1-3 microns. The polymeric binder material is substantially vehicle soluble although latexes are also eligible in some instances. Preferred water soluble binders include polyvinyl alcohol, hydroxyethylcellulose, methylcellulose, methyl(hydroxypropyl) cellulose, starch, modified starches, gelatin and the like. Eligible latex materials include polyacrylates, styrene-butadiene-rubber latexes, polyvinylacetates, polystyrene, and the like. The polymeric binder is used to protect the coated materials from brushing and handling forces occasioned by storage and use of thermal sheets. Binder should be present in an amount to afford such protection in an amount less than will interfere with achieving reactive contact between color-forming reactive materials.
Coat weights can effectively be about 3 to about 9 grams per square meter (gsm) and preferably about 5 to about 6 gsm. The practical amount of color-forming materials is controlled by economic considerations, functional parameters and desired handling characteristics of the coated sheets.
Electron-donating dye precursors are also known compounds. These electron donating dye cursors or chromogens include chromogenic compounds such as the phthalide, leucoauramine and fluoran compounds. These chromogenic materials or electron donating dye precursors are well known color-forming compounds for use in color-forming record systems. Examples of the compounds include Crystal Violet Lactone (3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide), (U.S. Pat. No. RE 23,024); phenyl-, indolyl, pyrrolyl, and carbazolyl-substituted phthalides (for example, in U.S. Pat. Nos. 3,491,111; 3,491,112; 3,491,116; 3,509,174); nitro-, amino-, amido-, sulfonamido-, aminobenzylidene-, halo-, anilino-substituted fluorans (for example, the U.S. Pat. Nos. 3,624,107; 3,627,78; 3,641,011; 3,642,828; 3,681,390); spirodipyrans (U.S. Pat. No. 3,971,808); and pyridine and pyrazine compounds (for example, in U.S. Pat. Nos. 3,775,424 and 3,853,869). Other specifically eligible chromogenic compounds, not limiting the invention in any way, are: 3-diethylamino-6-methyl-7-anilino-flouran (U.S. Pat. No. 4,510,513); 3-dibutylamino-6-methyl-7-anilino-fluoran; 3-dibutylamino-7-(2-chloroanilino) fluoran; 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-3,5xe2x80x26-tris(dimethylamino)spiro[9H-fluorene-9,1xe2x80x2(3xe2x80x2H)-isobenzofuran]-3xe2x80x2-one; 7-(1-ethyl-2-methylindole-3-yl)-7-(4-diethylamino-2-ethoxyphenyl)-5,7-dihydrofuro[3,4-b]pyridin-5-one (U.S. Pat. No. 4,246,318); 3-diethylamino-7-(2-chloroanilino)fluoran (U.S. Pat. No. 3,920,510); 3-(N-methylcyclohexylamino)-6-methyl-7-anilinofluoran (U.S. Pat. No. 3,959,571); 7-(1-octyl-2-methylindole-3-yl)-7-(4-diethylamino-2-ethoxyphenyl)-5,7-dihydrofuro[3,4-b]pyridin-5-one; 3-diethylamino-7,8-benzofluoran; 3,3-bis(1-ethyl-2-methylindole-3-yl)phthalide; 3-diethylamino-7-anilinofluoran; 3-diethylamino-7-benzylaminofluoran; 3xe2x80x2-phenyl-7-dibenzylamino-2,2xe2x80x2-spirodi-[2H-1-benzopyran] and mixtures of any of the following.
Examples of eligible acidic developer material include the compounds listed in U.S. Pat. No. 3,539,375 as phenolic reactive material, particularly the monophenols and diphenols. Eligible acidic developer material also includes, without being considered as limiting, the following compounds which may be used individually or in mixtures: 4,4xe2x80x2-isopropylidinediphenol (Bisphenol A); p-hydroxybenzaldehyde; p-hydroxybenzophenone; p-hydroxypropiophenone; 2,4-dihydroxybenzophenone; 1,1-bis(4-hydroxyphenyl)cyclohexane; salicylanilide; 4-hydroxy-2-methylacetophenone; 2-acetylbenzoic acid; m-hydroxyacetanilide; p-hydroxyacetanilide; 2,4-dihydroxyacetophenone; 4-hydroxy-4xe2x80x2-methylbenzophenone; 4,4xe2x80x2-dihydroxybenzophenone; 2,2-bis(4-hydroxyphenyl)-4-methylpentane; benzyl (4-hydroxyphenyl)ketone; 2,2-bis(4-hydroxyphenyl)-5-methylhexane; ethyl-4,4-bis(4-hydroxyphenyl) pentanoate; isopropyl-4,4-bis(4-hydroxyphenyl) pentanoate; methyl-4,4-bis(4-hydroxyphenyl) pentanoate; alkyl-4,4-bis(4-hydroxyphenyl) pentanoate; 3,3-bis(4-hydroxyphenyl) pentane; 4,4-bis(4-hydroxyphenyl) heptane; 2,2-bis(4-hydroxyphenyl)-1-phenylpropane; 2,2-bis(4-hydroxyphenyl) butane; 2,2xe2x80x2-methylene-bis(4-ethyl-6-tertiarybutyl phenol); 4-hydroxycoumarin; 7-hydroxy-4-methylcoumarin; 2,2xe2x80x2-methylene-bis(4-octyl phenol); 4,4xe2x80x2-sulfonyldiphenol; 4,4xe2x80x2-thiobis(6-tertiarybutyl-m-cresol); methyl-p-hydroxybenzoate; n-propyl-p-hydroxybenzoate; benzyl-p-hydroxybenzoate. Preferred among these are the phenolic developer compounds. More preferred among the phenol compounds are 4,4xe2x80x2-isopropylindinediphenol, ethyl-4,4-bis(4-hydroxyphenyl)-pentanoate, n-propyl-4,4-bis(4-hydroxyphenyl)pentanoate, isopropyl-4,4-bis(4-hydroxyphenyl) pentanoate, methyl-4,4-bis(4-hydroxyphenyl)-pentanoate, 2,2-bis-(4-hydroxyphenyl)-4-methylpentane, p-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 1,1-bis(4-hydroxyphenyl)cyclohexane, and benzyl-p-hydroxybenzoate. Acid compounds of other kind and types are eligible.
Examples of such other compounds are zeolites, phenolic novolak resins which are the product of reaction between, for example, formaldehyde and a phenol such as an alkylphenol, e.g., p-octylphenol, or other phenols such as p-phenylphenol, and the like; and acid mineral materials including colloidal silica, kaolin, bentonite, attapulgite, hallosyte, and the like. Some of the polymers and minerals do not melt but undergo color reaction on fusion of the chromogen.
The following examples are given to illustrate some of the features of the present and should not be considered as limiting. In these examples all parts or proportions are by weight and all measurement are in the metric system, unless otherwise stated.
In all examples illustrated in the present invention, a dispersion of a particular system component was prepared by milling the component in an aqueous solution of the binder until a particle size of between about 1 micron and 10 microns was achieved. The milling was accomplished in an attritor or other suitable milling device. The desired average particle size was about 1-3 microns in each dispersion.
Although some of the examples illustrate the invention using 2,2-bis (4-hydroxyphenyl)-4-methylpentane as the acidic developer material, the invention is readily practiced using any of the eligible acidic developer materials listed above.
The thermally-responsive sheets were made by making separate dispersions of chromogenic material, acidic material and the compound of formula I. The dispersions were mixed in the desired ratios and applied to a support with a wire wound rod and dried. Other materials such as fillers, antioxidants, lubricants and waxes can be added if desired. The sheets may be calendered to improve smoothness.
The thermal images are measured using a McBeth RD-922 densitometer. The densitometer is calibrated such that 0.08 indicates pure white and 1.79 a fully saturated black image.
Dispersions can be prepared in a quickie mill, attritor and small media mill. Optionally, but preferably dispersants can be added such as Nopco NDW at about 0.1 parts. This material is a sulfonated castor oil produced by Nopco Chemical Company. Surfynol 104 which is a di-tertiary acetylene glycol surface active agent produced by Air Products and Chemicals, Inc. could also be included, for example at about 0.4 parts. Additionally, water-soluble polymers other than polyvinyl alcohol (PVA) may be used to prepare the dispersions.